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Fixing bad Oscilloscope Waveform Shape caused by poor Interpolation

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bb1:
Attached pdf contains oscilloscope screenshots showing bad waveforms spoiled by poor interpolation at not high enough sampling rate.
The pdf describes very simple method to exchange long waveform length to high time resolution hugely exceeding sampling rate.
Very much improved waveform plot, limited only by the scope analog circuitry bandwidth, but not the sample rate, is shown.
Examples use waveforms captured by the RIGOL DS2000A scope, but the described method can be applied to any scope.

Multimetertools:
Poor interpolation can cause an oscilloscope to make waveforms that are not accurate or consistent. Interpolation adds extra points between existing points to provide better resolution and accuracy. When this process isn't done correctly, it can lead to incorrect measurements or distorted waveforms.

1. Understanding Interpolation:

It is essential to understand the concept of interpolation to successfully fix oscilloscope waveform shape caused by poor interpolation. Interpolation is adding extra points between existing points to provide more accurate resolution and measurement of signal behavior.



2. Identifying Poor Interpolation:

The first step in resolving oscilloscope waveform shape caused by poor interpolation is to identify the source of this problem. Visual inspection can determine if there are distortions within the waveform or if it appears jagged or uneven. Also, measurements like amplitude, frequency, and rise time can be taken at certain points on the waveform to see if bad interpolation is to blame.



3. Adjusting Interpolation Settings:

Once bad interpolation has been found to be the cause of the shape of the waveform, the next step is to change the interpolation settings on the oscilloscope. To get an accurate and consistent shape from different types of waveforms, you may need to use different interpolation settings. For example, a sine wave will require slightly different settings than a square wave or triangle wave. Experiment with various combinations of Interpolation type (Linear/Cubic) and Interpolator Length until an optimal waveform is achieved.



4. Troubleshooting Other Causes:

If changing the oscilloscope's interpolation settings doesn't make the waveform look better, it's important to think about what else could be wrong. Issues such as improper grounding, incorrect probe connection, or an interference source may be causing the distortion and should be thoroughly investigated and addressed.



5. Verifying Measurements:

Once the oscilloscope waveform has the shape you want, it's important to take accurate measurements to ensure it's right. At certain points on the waveform, you can check the amplitude, frequency, and rise time to ensure they are in acceptable ranges. If any of these numbers don't seem right, you may need to do more troubleshooting to fix the problem.



If you understand interpolation and follow these steps to fix bad oscilloscope waveform shape caused by bad interpolation, you can make accurate and consistent waveforms. This will give the most accurate readings and ensure the oscilloscope is used safely and well.

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2N3055:

--- Quote from: bb1 on March 03, 2023, 01:14:36 am ---Attached pdf contains oscilloscope screenshots showing bad waveforms spoiled by poor interpolation at not high enough sampling rate.
The pdf describes very simple method to exchange long waveform length to high time resolution hugely exceeding sampling rate.
Very much improved waveform plot, limited only by the scope analog circuitry bandwidth, but not the sample rate, is shown.
Examples use waveforms captured by the RIGOL DS2000A scope, but the described method can be applied to any scope.

--- End quote ---

Or you just buy Siglent scope and put it in a dot mode....

Research term ETS (Equivalent time sampling) Sequential Sampling and Random interleaved sampling...

nctnico:

--- Quote from: bb1 on March 03, 2023, 01:14:36 am ---Attached pdf contains oscilloscope screenshots showing bad waveforms spoiled by poor interpolation at not high enough sampling rate.
The pdf describes very simple method to exchange long waveform length to high time resolution hugely exceeding sampling rate.
Very much improved waveform plot, limited only by the scope analog circuitry bandwidth, but not the sample rate, is shown.
Examples use waveforms captured by the RIGOL DS2000A scope, but the described method can be applied to any scope.

--- End quote ---
It doesn't have to be applied to any scope because most oscilloscopes have sin x/x reconstruction (it is not interpolation!) implemented correctly. But it is not out of the ordinary to find improper sin x/x implementations in alpha version DSO firmware so I guess Rigol is not an exception.

@2N3055: again, dot mode is not ETS (equivalent time sampling). There is much more to ETS than just plotting some dots on screen. For starters ETS will take a known / predictable amount of samples per time interval. Or put differently: the effective samplerate is pre-determined which you won't get with dot mode.

bb1:
Quotes from the Tektronix User manual:
"Your oscilloscope can interpolate between the samples it acquires. Like for
equivalent time sampling, it does so only when it cannot obtain all the real
samples it needs to fill up its waveform record."
"Sin(x)/x interpolation computes record points using a curve fit between the actual
values acquired."

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